The present invention relates to permanent magnetic motor drives. In particular, the invention relates to procedures in such drives for handling faults when detected.
Three-phase voltage inverters are commonly employed to the control the magnitude and frequency of the motor phase currents in hybrid vehicles (including electric and fuel cell powered). When the ac motor used is of the class of interior permanent magnet (IPM) type, the reaction of the system to various inverter based faults is of concern since the fault may cause an uncontrolled breaking torque in the motor.
Drive system faults can be classified as short-circuit type faults and open-circuit type faults. The behavior of various faults in permanent magnetic motor drives has been reported in the literature for many years. Modeling and system behavior of short-circuit type faults are described in B. A. Welchko, T. M. Jahns, W. L. Soong, and J. M. Nagashima, “IPM synchronous machine drive response to symmetrical and asymmetrical short circuit faults,” IEEE Trans. Energy Conversion, vol. 18, no. 2, pp. 291-298. June 2003.
For inverter driven IPM motors, an important class of open-circuit type faults results when the control gate signals to all of the six inverter switches are turned off, or disconnected. During this condition, the motor is connected to the dc source (e.g., battery, fuel cell, etc.) via the antiparallel diodes of the inverter switches. The antiparallel diodes create a potential path for current to flow which is dependant upon the motor operating condition and dc source voltage. The fault condition where the six gate signals have been turned off has been termed an uncontrolled generator mode (UCG mode) of operation since the motor would operate during the condition as a generator converting rotational power into electric currents. Modeling and system behavior during UCG mode operation is characterized in T. M. Jahns and V. Caliskan, “Uncontrolled Generator Operation of Interior PM Synchronous Machines Following High-Speed Inverter Shutdown,” IEEE Trans. Industry Applications, vol. 35, no. 6, pp. 1347-1357, Nov./Dec. 1999.